CN1639445A - Methods for controlling screenouts - Google Patents

Abstract

Methods are presented to induce a screenout during a subterranean formation fracturing or combined fracturing and gravel packing treatment by laying down a filter cake early in the treatment, then injecting proppant slurry, and then while proppant slurry injection continues chemically damaging the filter cake with one or more filter cake degradation agents, and optional filter cake degradation agent aids, so that leak-off increases, the concentration of proppant in the fracture increases, and the proppant screens out. The additional use of bridging-promoting materials, alone or in conjunction with filter cake degradation, is included.

Description

Method for controlling the sieve

technical field

The present invention relates to increasing the flow of fluids into or out of a subterranean well. More specifically, the present invention relates to facilitating the flow of fluids from a rock formation into a wellbore. In particular, the present invention relates to methods for performing fracturing and gravel during hydraulic fracturing (conventional or utilizing coiled tube), during fracturing followed by gravel packing, or in one operation. The method of controlling the size, shape, position and quality of the cracks formed during the filling process.

Background technique

Hydraulic fracturing, gravel packing, or the combination of fracturing and gravel packing in one operation, are widely used to facilitate the recovery of hydrocarbons, water, or other fluids from a formation. These operations involve pumping "proppant" slurries (natural or synthetic materials used to prop up fractures after they have formed) during hydraulic fracturing or "gravel" during gravel packing. In highly permeable formations, the goal of hydraulic fracturing treatments is usually to create short, wide, highly conductive fractures in order to bypass areas of damage to nearby wellbores during drilling and/or completion , thereby ensuring good communication between the formation and the wellbore, thereby increasing the surface area available for fluid flow into the wellbore. Gravel can also be a natural or synthetic material, which can be the same as or different from the proppant. Gravel packs are used for "sandy" control. By sand is meant any particulate matter from the formation, such as earth, that is carried into mining equipment. Gravel packing is a sand control method used to prevent the mining of formation sand. In this sand control method, a steel screen is placed in the wellbore and the surrounding annular space (annulus) is filled with prefabricated These prefabricated gravels are sized to prevent the passage of formation sand that would clog underground and surface equipment and reduce flow. The primary purpose of gravel packing is to stabilize the formation while minimizing damage to the productivity of the well.

Sometimes, gravel packs are done without screens. Highly permeable formations are often poorly consolidated and, therefore, require sand control. Thus, a hydraulic fracturing treatment is often combined in a single continuous operation (fracturing and packing) with gravel packing, which is used to create short, wide fractures. For the sake of brevity, in the following description we may only refer to hydraulic fracturing, fracturing and gravel packing in one operation (frac and pack), or any of gravel packing, however, meaning All of the above operations.

Packing of the wellbore with proppant or gravel in the upper portion of the production formation is undesirable. If this undesired phenomenon occurs, the wellbore must be cleared so that various other running operations, such as placing tools, etc., can be performed so that fluids can be optimally recovered. Furthermore, if this operational screening is carried out too late or not at all, i.e. if the fissure continues to grow such that the length and/or height of the fissure exceeds what is needed and expected, then optimum performance will not occur. The filling and desired fracture size and shape, which can not increase production, nor prevent proppant or sand flowback (flowback), this situation is very unfavorable.

As said, short and wide slits are desired. However, short and wide fractures are not always achievable with conventional fracturing treatments. The most common method for intentionally creating short and wide slits is to induce a tip screenout (TSO) during pumping operations. In the end screen, due to fluid leak-off into the formation, the solids concentration becomes so great at the end of the fracture that the slurry no longer flows. This concentrated proppant slurry plugs the fracture and prevents the fracture from growing further. After the screen is formed, the proppant/fluid slurry is re-pumped into the formation so that the fractures become wider and a large concentration of proppant per surface area is placed in the fractures. The equipment for these treatments relies on knowledge of the exact mechanical properties, permeability, reservoir pressure and fluid saturation of the formation being treated. Prior to performing most of these treatments, small fracturing treatments (sometimes referred to as "data fracturing" or "mini-fracturing") are performed in order to measure these properties and the formation's response to these hydraulic fracturing treatments. These treatment designs are often modified on the fly to take advantage of this new information. Important design parameters are: pad size, size and number of stages, proppant or gravel concentration in each subsequent stage, properties of fluids, properties of additives used in each stage. Such process design and modification is typically accomplished with the aid of computer models available in the industry.

Pack refers to a proppant-free fluid that is pumped to initiate and extend a fracture prior to some stage including the application of proppant or gravel. Such fillers usually have another function, forming a coating on the surface of the formed fissures, which is called a "filter cake". This filter cake reduces the fluid flow from the fractures into the formation (affecting the "efficiency" of the work (see description below)). Filter cakes can be made from viscous agents, typically, for example, polymers. For that purpose, especially if the pores of the fracture surface are large, the filter cake can also be made by adding some additive material to the fluid used to form the filter cake. In this use, the selectively added material is often referred to as a fluid loss control additive or FLA.

During hydraulic fracturing, especially in low-permeability formations, it is desirable to have as long a fracture as possible (in order to form a fracture surface as large as possible for fluid to flow into the fracture and eventually into the wellbore), in order to obtain Long conductive fractures generally avoid operating modes that cause end-sieves. If an end screen condition occurs during such a fracturing operation before the entire design treatment fluid is pumped, as evidenced by an increase in hydraulic pressure, then the pumping rate is reduced, or , processing is most likely to be stopped and such processing is therefore considered invalid. We will refer to this type of hydraulic fracturing job design and job execution in which end screens are not desired and do not occur as "traditional" pressure fracturing.

On the other hand, it is sometimes desirable to have an end screen. Design features typically employed in special cases where it is desired to have terminal screens often involve methods that ensure that fluid leakage is high relative to the rate and volume of proppant injection. This can be achieved by utilizing small packs, utilizing little or no fluid loss additives, utilizing higher concentrations of proppant earlier in the treatment, slower pumping methods, and utilizing pressure/gravel pack in the field of fracturing and combined methods known to those of ordinary skill in the art.

Unfortunately, despite the data fracturing information collected by downhole pressure gauges during treatment, pressure instantaneous values indicate that TSO does not occur in many, if not most, treatments where it is desirable to have a TSO. screen. Fluid remains mobile at the ends of the fractures, which continue to grow throughout the treatment and, as a result, the desired concentration of proppant in the fractures is not achieved. Therefore, long and thin fissures are formed, and thus, desired fissure conductivity cannot be obtained. Typically, when end-screening is desired, end-screening must be induced by either decreasing the pumping rate or increasing the proppant concentration.

There are two main reasons why proper end-of-line screening cannot be achieved. The first reason is that the fracture may be too large for the proppant volume. Failure to achieve proper end screening occurs a) when the packing is too large, or b) when the efficiency is too high, or c) when the ratio of proppant volume to slurry volume is not high enough in the job design. (The "efficiency" of a fracturing operation is high when fluid leakage is controlled to an acceptably low level by fluid and matrix properties or by the addition of fluid loss control additives; inefficient when the level of leakage is high , so that very large volumes of fluid must be pumped in order to create the desired fracture size and shape and place the specified amount of proppant or gravel.) The second reason is that the fracture width may be too large for the A bridge cannot form in the chasm. This could be due to poor initial design (eg, poor design in choosing the proppant diameter) or an increase in width beyond desired values.

Until now, the main way to deal with these issues, other than better job design, has been to optimize the choice of fluid loss control additives and the job stages in which they are used, especially if the main problem is proppant The case where the crack is too large in terms of volume.

Fibers are used to control proppant flowback during fracturing. In this case, fibers are added at an optimal concentration to control proppant flowback without significantly affecting fracture conductivity. If glass fibers are utilized, for example, this concentration is on the order of about 1% by weight of the proppant. Where glass fibers are normally used, especially in low permeability formations, this concentration is insufficient to cause bridging during pumping. Fibers are also sometimes used to aid proppant transport when the fluid viscosity is very low. In these treatments, end screens are often deliberately avoided; proppant concentrations are kept low by careful design of the pretreatment job, especially the choice of pumping time. For example, during these treatments, on conventional job designs, the packing volume is increased to ensure sufficient fracture width before the proppant/fiber slurry enters the fracture.

Since the true nature of the formation is unknown and variable, the ability to successfully obtain end screens is largely uncertain. Ideally, some way would be available to cause end-sieves when they are needed and to cause end-sieves more depending on the characteristics of the job under the operator's control (especially the fluids and fluids used loss control additive chemistry), rather than depending on the unknown variability of the formation. Therefore, there is a need for some more reliable means of ensuring that the desired end-sieving will occur in order to allow greater flexibility in designing end-sieving treatments.

Contents of the invention

In one embodiment, when end sieving is desired to occur, end sieving is caused by adding a bridging promoter to the proppant slurry. In another embodiment, the bridging-promoting agents are fibers that are added to the proppant slurry at concentrations higher than those commonly used for flowback control and which are added early in the process , in order to cause proppant bridging and cause end screens during pumping. Another embodiment of the present invention is to intentionally induce terminal sieving by using high concentrations of bridging promoters early in the stimulation treatment. Another embodiment of the present invention is to intentionally induce end-screening in combination stimulation/gravel pack treatments, especially during hydraulic fracturing/gravel pack, by using high concentrations of bridging promoters early in the treatment. Another embodiment of the present invention is to intentionally induce end screens in a combined stimulation/gravel pack process using annular screens by using a high concentration of bridging promoter early in the process. Another embodiment of the present invention is the use of appropriate selection of process parameters to increase the likelihood of terminal sieving, in addition to the use of high concentrations of bridging promoters early in the process, thereby causing terminal sieving. Further examples are prior methods in which bridging promoters are added later in the process. Another embodiment is a proppant slurry comprising sufficient bridging promoters to allow the slurry to sieve when the bridging promoters are injected into the fracture.

Another embodiment of the invention is a method of stimulating a formation by propping a fracture, by forming a filter cake, and then utilizing one or more filter fluids while injecting proppant into the fracture. A cake degrading agent is used to degrade the filter cake to form a filter screen. In some embodiments, the filter cake is made from a viscosifier used in the slurry carrier fluid, or from a fluid loss additive, or from a combination of said viscosifier and a loss additive. Forming. In some embodiments, the filter cake degrading agent can be an oxidizing agent, an enzyme, an acid, or a mixture thereof. Another embodiment is a method of forming a screen during stimulation of a formation, wherein the stimulation includes injecting a slurry of proppant into a carrier fluid at a pressure above the fracturing pressure to form one or more fractures, the The method includes: injecting a packing fluid for forming a filter cake; injecting one or more first slurry stages comprising proppant in a carrier fluid, degrading the filter cake with a filter cake degrading agent, and simultaneously injecting one or more A second slurry stage of proppant in the carrier fluid. In other embodiments of this method, said packing fluid includes one or more of a fluid loss additive, a filter cake degrader, a filter cake degrader adjuvant, and mixtures thereof, so long as For the degradant, it is sufficient not to include a filter cake degrader adjuvant therefor; one or more first slurry stages include one of a fluid loss additive, a filter cake degrader, a filter cake degrader adjuvant, and mixtures thereof One or more, as long as, for the degradation agent included, there is no adjuvant for which the filter cake degrader is included in the first slurry stage, or there is no filter cake degrader adjuvant in the packing; said one The or more second slurry stages include one or more of a filter cake degrader, a filter cake degrader adjuvant, and mixtures thereof. In additional embodiments, both the packing fluid and the one or more first slurry stages include a fluid loss additive, a first filter cake degrader, and a filter cake degrader adjuvant for a second filter cake degrader, at process conditions Here, the second cake degrading agent is more active than the first cake degrading agent; and the one or more second slurry stages contain the second cake degrading agent. In additional embodiments, the filter cake includes a polymer that is susceptible to enzymatic and oxidative degradation under processing conditions; the first filter cake degrading agent is present in the filler and includes a enzyme; the second cake degrader is present in one or more second slurry stages and includes an oxidizing compound for degrading the polymer; for the second cake degrader, the second cake degrader assists The agent is present in one or more filler fluids, one or more first slurry stages, one or more second stages, and is a tertiary amine. In another embodiment, the filter cake comprises acid soluble solid particulate compounds, the second filter cake degrading agent is present in one or more second slurry stages and includes an acid, and under process conditions, the The acid is capable of at least partially dissolving the acid-soluble solid particulate compound. In additional embodiments, the one or more filler fluids, the one or more first slurry stages, and the one or more second slurry stages include a bridging promoting material. In a preferred embodiment, the filter cake comprises a polymer which is susceptible to enzymatic and oxidative degradation under processing conditions; the first filter cake degrading agent is present in said packing and comprises an enzyme which an enzyme degrades said polymer; a second filter cake degrader is present in one or more slurry stages and includes an oxidizing compound which degrades said polymer; for the second filter cake For the degradant, the second filter cake degrader adjuvant is present in the one or more filler fluids, in the one or more first slurry stages, and in the one or more second slurry stages, and is a tertiary amine; and at least a portion of said one or more first slurry stages comprise a bridging promoting material. In another embodiment, a sand control screen is placed prior to treatment. In other embodiments, the treatment is a combined fracturing/gravel pack treatment. Additional embodiments of the present invention provide methods for inducing end-sieves during processing that would otherwise be difficult, expensive, inefficient, or even non-existent. An end screen may be introduced, which would provide the operator with an additional means for controlling the process.

Description of drawings

Figure 1 shows typical fluid leakage volume data with and without fluid loss additive.

Figure 2 is a schematic diagram of the depth of leakage fluid penetration into the formation with and without leakage additive.

Figure 3 shows the dynamic fluid loss volume and fluid viscosity as a function of time in some experiments using two different combinations of fluid loss additive, filter cake degrader and filter cake degrader adjuvant.

Figure 4 shows the dynamic fluid loss volume and fluid viscosity as a function of time for one experiment where fluid loss additive addition was stopped and no cake degrader or filter cake degrader adjuvant was present.

Figure 5 is a schematic diagram showing the effect of the addition of fluid loss additive, fiber, cake degrader and cake degrader adjuvant on fracture formation.

Description of the preferred embodiment

For an aid in understanding the deliberate end screens created by working design during hydraulic fracturing and combined fracturing/gravel pack operations, see M. Economides and K. notle, eds., Reservoir Stimulation, 3 rd edition , John Wiley & Sons, Ltd, New York (2000) pp 10-21 to 10-24; and F.L.Monus, F.W.Broussard, J.A.Ayoub and W.D.Norman, "Fracturing Unconsolidated Sand Formations Offshore Gulf of Mexico," SPE 24824), (199 We have found that we can create a situation in which the slurry in the fracture is no longer flowable by changing one or both of the two properties of the slurry. By adding an immobilizing material other than proppant, the solids can be altered so that the slurry no longer flows at lower concentrations than the slurry would no longer be flowable without the addition of the material. Is flowable, or, can increase fluid leakage, thereby increasing the concentration of solids, or both. We have found ways to controllably and deliberately create screens in fractures through manipulation of the composition of the injected fluid and/or through the addition of bridging promoting materials such as fibers. A method that is particularly effective when the reason for sieving is due to fractures that are too large for the proppant volume is to form a filter cake and then reduce the size of the filter cake at the appropriate time or Increased permeability. We use the term filter cake degradation to include reducing the size of the filter cake or increasing the permeability of the filter cake by cracking or dissolving at least a portion of at least one component of the filter cake. This can be done, for example, by working with one or more suitable breakers or dissolvers to crack or dissolve the filter cake, which we call filter cakes. Cake degrading agent, sometimes this filter cake degrading agent has an additional splitting agent or dissolving agent adjuvant, we call this splitting agent or dissolving agent adjuvant as filter cake degrading agent adjuvant. The lysing or dissolving agent may be delayed, for example by means of a delaying agent or by encapsulation. When the fracture is too large for the proppant volume, one or more cracking or dissolving agents are added throughout the job or at least during the packing and/or early stages of the job.

Other methods are particularly effective when the failure to screen is due to a fracture that is too wide for the bridging proppant. An example of this is by adding an appropriate lysing agent, sometimes with a lysing agent adjuvant, or by adding multiple lysing agents or a better lysing agent at a later stage of the work. agents to reduce efficiency in later stages of work. In this embodiment, no cracking agent may be used during the packing or during the early support stages. These cracking agents are effective when the filter cake's resistance to fluid flow is primarily due to polymers in this fluid or in fluid loss control additives (FLAs).

If the filter cake's resistance to fluid flow is primarily due to calcium carbonate or one or more other acid soluble materials in the fluid loss control additive, the filter cake can be dissolved by adding acid in a later stage.

Another approach is to add fibers or other materials (known as bridging-promoting materials) to the proppant to aid in bridging, which can be used alone or in combination with the basic one above for cracking or dissolving the filter cake. method combined. Sieving begins with bridging, that is, the solids in the fracture stop moving, while the liquid continues to flow; at a given location in the fracture, important parameters affecting the tendency to bridge are the particle size and shape distribution in the slurry, the fracture width and Volume concentration of proppant. Addition of bridging promoting material has a direct effect on bridging; deliberate disruption of the filter cake during processing can affect proppant concentration.

These methods involving cracking and dissolving the filter cake and adding fibers can be combined simultaneously or sequentially. These methods can also be used to deliberately create wider fractures with greater fracture conductivity. These methods can also be used as a form of diversion, that is, the operator can deliberately stop the growth and filling of a fracture and cause a new fracture without zonal isolation. These methods destroy the fluid loss control additive (FLA) throughout the fracture or only in a portion of the fracture. By speeding up leaks, optionally by aiding in bridging, the operator can determine and control when and where to create screens (thereby avoiding undesired results of not producing screens, can avoid very slow and inefficient screening results, It can also avoid the result of screen generation in the wellbore above the formation).

The important and unifying concept of these methods involving filter cake degradation is to include the degradation of the filter cake, laying down a filter cake early in the process, then injecting the proppant slurry, and then as the proppant slurry continues to be injected, it is degraded by the filter cake degradation agent The filter cake undergoes a chemical change that increases leakage and increases the concentration of proppant in the fracture, allowing proppant sieving. Depending on such factors as the reactivity of one or more filter cake degrading agents used under process conditions (e.g., temperature and pH of the carrier fluid), the thickness of the deposited filter cake (e.g., carrier fluid viscosity and formation Permeability), and other job design parameters such as job schedule, fracture size, proppant particle size, and timing of adding various chemicals will vary. For example, the pumping time of the packing must be long enough and/or contain enough fluid loss control additives to ensure the desired filter cake release. Cake degradation must not start too quickly nor too quickly that sieving occurs before it is expected to occur. Conversely, filter cake degradation must not start so slowly nor too late that sieving occurs too late or not at all. Addition of proppant is usually done in multiple stages. In each stage, a specific concentration of proppant is injected for a specific amount of time. Successive stages typically have successively increasing proppant concentrations. The proppant concentration can also be varied smoothly in a ramped fashion, that is, the proppant concentration increases continuously during the proppant pack phase. To facilitate description, a typical job will be divided into a packing phase and two sets of proppant slurry phases. During the packing stage, fissures are started to form and the filter cake is let down. In the first set of stages, the fissures are enlarged. In the second set of stages, screens are created and the fractures are filled with proppant. As said, some other characteristics of the job can strongly influence when to add chemicals. If the packing has to be very small, the cake lowering process can continue throughout or early in the first set of stages. If the filter cake degrader works slowly and can even start to be added in the filler stage, then degradation can start in the first set of stages. If the filter cake degrader acts very quickly, it may only be added during the second set of stages. A filter cake degrading agent of increasing reactivity may be used, or a filter cake degrading agent which degrades different components of the filter cake may be used simultaneously or sequentially. If the filter cake degrader is not sufficiently reactive, then a filter cake degrader adjuvant can be added. The filter cake degrader adjuvant can be added before or after the addition of the filter cake degrader and in such a way that the filter cake degrader and the Cake degrader adjuvant, or, cake degrader and cake degrader adjuvant added together in the second set of stages. In all fillers and some stages a bridging promoter can be added. Within the scope and contemplation of the present invention, one of ordinary skill in the field of formation stimulation can do so in many ways, depending on factors such as availability of chemicals and materials, availability of equipment and ability to add chemicals and materials, cost, etc. There are several different ways to design a treatment that produces fractures with specific end parameters such as size and conductivity.

Preferably, the present invention is practiced by first considering information about the well, formation, available fluids, and criteria for successful fracture stimulation, and then devising an optimized design for to increase the performance of the stimulated well. This design involves injecting an amount of a selected packing fluid and an amount of a selected fracturing fluid. This is usually done by analysis using fracture design and evaluation software, where pressure gradients are combined with algorithms for fracture length and height progression, complete leak information, the effects of multiple fluid injections and its temperature variation. For hydraulic fracturing or gravel packing or a combination of both, polymers (usually cross-linked with boron, zirconium or titanium compounds) or viscoelastic surfactant structures ("VES structures") are used to Aqueous fluids used for fillers or for forming slurries are viscosified, wherein the viscoelastic surfactant structure is formed using specific surfactants that form micelles of appropriate size and shape. Any fracturing fluid or gravel packing fluid can be used in the present invention, as long as they can be compatible with the special material of the present invention (fluid loss control additive, fiber, cracking agent, cracking agent auxiliary agent), and can be compatible with formation, support The agent and the desired treatment result are suitable. Thus, said fluid may for example be an aqueous based fluid or an oil based fluid, acidic or basic, these fluids may contain one or more polymers, viscoelastic surfactants or gelled oils. Polymers can be crosslinked. The methods of the present invention can be used for the original job design, or, the job can be designed without an end screen, and then, during job execution, it can be determined that an end screen is needed, so that the job to modify. (Note that in this specification, we often refer to any terminal screen as a terminal screen (TSO), however, a terminal screen means a screen that is produced in a fracture, not necessarily at the end of the wellbore. screens produced in the ends of distant fractures; the key is to generate said screens at the desired time and location rather than in the wellbore)

We use the term "conventional fracturing" here to refer to a hydraulic fracturing in which no end screen is desired or desired. We use the term "end screen" to mean a screen not in the wellbore but in the fracture but not necessarily in the end of the fracture away from the wellbore. In traditional fracturing, it is about avoiding modes of operation that can lead to end-of-the-line screens. If an end screen is encountered in a conventional fracturing operation, this can be deduced from the increase in pumping pressure before the entire design treatment is pumped, then adjustments can be made to operational parameters such as pumping rate or proppant concentration. Change in order to minimize the possibility of terminal sieving. However, such processing is often stopped and considered a failure.

The filler of the present invention comprises a carrier fluid and a viscosifying polymer or viscoelastic surfactant. It may additionally contain other additives commonly used in these fluids, as long as the composition of the pack does not cause damage to the formation or fracturing fluid. In the present invention, the fluid used as filler may generally contain substances such as anti-corrosion agents, friction reducers, soil stabilizers, scale inhibitors, biocides and the like.

The carrier fluid provides a medium for transporting other components into the formation. Preferably, said carrier fluid is water or saline. Selected organic or inorganic salts or mixtures may be included so long as they are compatible with the packing, fracturing fluid, formation and components of the formation fluid. A solution containing about 1% to 7% by weight of potassium chloride (KCl) or ammonium chloride is typically utilized as the base liquid in the fracturing fluid and packing to stabilize the soil and prevent it from swelling. Sometimes, other saline or seawater can be used. An organic cationic salt such as tetramethylammonium chloride is an effective salt at about 0.2-0.5 weight percent, but not limited thereto.

Generally, if the polymer is used to viscous the fluid, the polymer is water soluble. Commonly used effective water-soluble polymers include: polyvinyl polymers, polymethacrylamides, cellulose ethers, polysaccharides, lignosulfonates, amines, alkali metals, and their alkaline earth salts. Some specific examples of typical water-soluble polymers are: acrylic acid-acrylamide copolymer, acrylic acid-methacrylamide copolymer, polyacrylamide, partially hydrolyzed polyacrylamide, partially hydrolyzed polymethacrylamide, Polyvinyl alcohol, polyvinyl acetate, polyalkylene oxide, carboxylated cellulose, carboxyalkyl hydroxyethyl cellulose, hydroxyethyl cellulose, galactomannan (eg guar gum), substituted Galactomannans (e.g., hydroxypropyl guar, carboxymethylhydroxypropyl guar, and carboxymethylguar), heteropolysaccharides obtained from the fermentation of starch-derived sugars (e.g., xanthan gum), and their ammonium and alkali metal salts. Preferred water-soluble polymers include hydroxyethylcellulose, starch, sclerosing dextran, galactomannan and substituted galactomannan.

The optimum polymer concentration can be determined by selecting the desired leakage parameters and measuring the leakage using a sample of the desired fluid and a sample of the formation or a rock sample similar to the formation. Spills are defined by three terms: "spurt," which refers to the initial rapid leak of fluid before a filter cake barrier forms on the frac's face, and is measured in gallons per 100 square feet, for subsequent Leakage occurs even after filter cake formation and the parameters that can be controlled by viscosity and wall-building propensity are: wall-building fluid loss coefficient Cw and viscosity-controlling fluid loss coefficient Cv. Cw is not applicable if no wall building material is present. Cv is not suitable if it has a low, limited Cw. Cw and Cv are measured in ft/min1 ^/2 . "Spray", Cw and Cv have preferred values of 0 to about 5, about 0.001 to about 0.05 and about 0.001 to about 0.05, respectively; more preferred values of 0 to about 2, about 0.001 to 0.008 and about 0.001 to 0.008; most preferred Values are 0 to 1, about 0.001 to 0.003 and about 0.001 to 0.003. The values of these parameters (and the actual behavior they represent) can vary significantly so long as the proper filter cake is produced at the proper time. An experimental method for determining these values is given in the following article: Navarrete, RC, Caweizel, K, E., and Constien, VG: "Dynamic Fluid Loss in Hydraulic Fracturing Under RealisticShear Conditions in High Permeability Rocks", SPE Production and Facilities, pp138-143 (August, 1996).

Any viscoelastic surfactant based fluid that is compatible with the formation, formation fluids, any additives during and/or after packing can be used. Some particularly effective fluids are described in US5551516, US5964295; US5979555; US5979557; US6140277; US6258859. Splitting agents can also be used in viscoelastic surfactants.

In some of the methods of the present invention wherein the filter cake is disrupted or weakened in part or primarily by properly timed positioning, the packing and/or proppant loading stage preferably also includes one or more fluid loss control additives so that A suitable filter cake is formed. If they do not contain polymeric materials capable of forming a suitable filter cake, for example, if viscoelastic surfactants are utilized to viscous the frac packing and/or carrier fluid, then the packing and/or proppant carrier stages must contain one or Wide range of fluid loss control additives for proper filter cake formation. The fluid loss additive may be, for example, but not limited to, a water-soluble polymer or a cross-linked water-soluble polymer. If a polymer or cross-linked polymer is used to viscose the packing and/or proppant-laden fluid, then the fluid loss control additive may be the same or a different polymer or cross-linked polymer. The amount needed to viscosify the carrier fluid may be sufficient, or more may be added to form a proper filter cake. Fluid loss control additives can also be solids such as asbestos, granular starch, calcium carbonate (calcite), granular mica, plastic particles, solid wax or wax-polymer particles, solid oil-soluble resin particles, insoluble salts , slowly soluble salts (eg, sodium chloride, provided the carrier fluid and formation water have high ionic strength), and mixtures thereof. Fluid loss control additives must contain at least one ingredient that can be cleaved or degraded (e.g., polymer oxidation, or enzymatic degradation of cross-linked natural polymers) or dissolved (e.g., by acid treatment of calcium carbonate dissolving, or using solvents to dissolve waxes or resins).

The present invention is practiced by first determining the fluid loss control additive and cracking agent or cracking agent (preferably with cracking agent adjuvant) or dissolving agent (such as acid) by experiment and then often by computer simulation and modeling. ) and determine the stages that should include these amounts so that cracking and dissolution of the filter cake occurs at the desired time and place. One of ordinary skill in the art of subterranean well stimulation can readily accomplish this with knowledge of the chemicals and conditions, especially the times and temperatures involved. This process can be accomplished, for example, by adjusting the chemistry and/or working pumping design or both, including in an iterative manner, usually by simulation, until the desired result is predicted. We refer to these materials that are used to crack or dissolve filter cake and/or fluid loss additives as "filter cake degradants". In some embodiments, no fluid loss control additives may be added and the filter cake may be formed by viscosifiers alone. In other embodiments, for example, when a viscoelastic surfactant is used to viscose the fluid, the filter cake may be formed entirely of one or more fluid loss control additives. In a preferred embodiment, the packing and optional first proppant-laden stage comprises a first cracking agent and a cracking agent adjuvant (eg, which may be a catalyst) for a second cracking agent. Subsequent stages contain a second lysing agent. These lysing agents and lysing agent adjuvants may be solid or liquid and may be delayed (eg by encapsulation). The intermediate stage may contain two cleavage agents or two cleavage agents plus a lysis agent adjuvant for the second lysis agent, or only the second lysis agent and its lysis agent adjuvant. Thus, when the second splitting agent contacts the filter cake, the filter cake already contains a splitting agent adjuvant for the second splitting agent. Thus, each stage of the job (pack, early proppant stage, late proppant stage) can contain various combinations of fluid loss control additives, different cracking agents, cracking agent adjuvants for different cracking agents. The lysing agent adjuvant can be pumped before, while, or after the lysing agent it acts on is used. The materials used to form the filter cake will always be either fillers, or viscosifiers (polymers or cross-linked polymers) or added fluid loss control additives. It is not necessary for the cracking agent to be present in the filler, especially if the temperature is high enough that at least some natural degradation occurs. Similarly, fluid loss control additives need not be present in all or some of the proppant-containing stages if a satisfactory filter cake has formed. All of these methods are counter to common practice in which it is desirable to keep fluid efficiency as high as possible until stimulation is complete.

If the filter cake is degraded by dissolution of an ingredient (e.g., but not limited to, calcium carbonate), this can be achieved by, in appropriate stages or stages, , cross-linked polymers or viscoelastic surfactants (all of which are neutralized and combined with acids in the prior art) to accomplish this. A suitable acid may be any acid known in the art for dissolving calcium carbonate, such as, but not limited to, mineral acids such as hydrochloric acid, hydrofluoric acid, and mixtures of these two acids. Organic acids can also be used, such as but not limited to: formic acid, acetic acid, fluoboric acid, citric acid, these organic acids can be used in combination with inorganic acids, can also be used alone. Additive materials such as chelating agents can be used to increase the solvency of the acid. For example but not limited to: amino polycarboxylic acid, such as ethylene (ethylene) diamine tetraacetic acid (ethylenediamine tetraacetic acid), diethylenetriaminepentaacetic acid (diethylenetriaminepentaacetic acid) and their mixtures.

This use of acid to dissolve the filter cake during a fracturing job is in contrast to what is typically done during conventional fracturing where removal of the filter cake during a job is not expected. For example, there are known methods for acid fracturing in which the packing and acid stages are alternated. Each packing stage contains a fluid loss control additive or polymer or emulsion to form a filter cake that blocks areas of the matrix (matrix) that have been attacked by acid (or where with holes) and transfers the acid to a portion of the substrate that was not previously attacked by the acid. In this application, acid removal of the filter cake is undesirable.

It is generally desirable to degrade the filter cake after stimulation in order to minimize damage to the fracture surface "skin" and to maximize fluid flow from the matrix into the fracture and ultimately the wellbore. This degradation, albeit slowly, usually occurs naturally, either by thermal processes, or by dissolution of the filter cake in typical slurry fluids, or by physical processes, especially due to reverse flow (the reversal of flow) (during processing, the fluid flows out of the fracture and into the formation, and at the start of production, said fluid flows out of the formation and into the fracture). Filter cake degraders have not previously been employed to cause very rapid filter cake degradation during hydraulic fracturing treatments. Because the filter cake is deliberately degraded by the method of the present invention, the degradation can be made faster, thus greatly increasing the rate of fluid recovery.

Currently, one way to prevent end-screening is to design the job so that the fracture is too wide for bridging with the size of proppant used. Instead, one approach used to facilitate end-screening is to add a material that facilitates or promotes bridging and prevents proppant movement in the fracture. We have found that certain materials, when added to proppant slurries in sufficient concentrations, promote or assist bridging of proppant particles (by significantly increasing and strengthening the degree of interaction between particles) and make Movement of proppant in the fracture ceases. We refer to these materials as "bridging-promoting materials" or bridging-promoting agents. We have found that during a job, whether or not the job is designed for an end screen, end screens can be induced by adding an appropriate amount of bridging promoting material to the proppant slurry. Although we will use fibers as an example to describe embodiments of the invention, other materials can also be used as bridging promoters, for example, needles, fibrils, platelets, irregular particles, flakes, strips , especially, but not limited to, materials having an aspect ratio greater than about 3, most preferably having an aspect ratio greater than about 300. Any organic and inorganic, natural or synthetic materials are suitable so long as they reduce the fluidity of the fluid/proppant slurry when dewatered. Materials with aspect ratios greater than about 3 are preferred because these materials result in greater permeability to the proppant pack. Particularly suitable materials are disclosed in US Pat. Nos. 5,330,005, 5,439,055, 5,501,275, and 5,782,300, which are incorporated herein by reference, but said materials are not limited thereto. In a single treatment, more than one bridging promoting material may be used simultaneously or sequentially. The material used to make the bridging promoter is not a critical variable, as long as the flow reducer does not chemically react with other components in the fluid in which it is used, and the flow reducer is The environment is stable and the flow reducer and the slurry containing the flow reducer can be handled, mixed and pumped with available equipment. The following description is primarily based on the method of utilizing bridging promoting material as a method of promoting terminal screening, however, it should be understood that the concepts of adding bridging promoting material and filter cake formation/degradation can be combined simultaneously or sequentially.

In traditional hydraulic fracturing, fibers are used to prevent proppant flowback, that is, to keep proppant in the fracture so that it cannot be extracted with fluids. This allows more intense (higher rate) flowback of fracture fluids and produced hydrocarbons without proppant flowback. Resin-coated proppants are used for the same purpose, however, fibers are generally better. In M. Economides and K. Nolte, eds., Reservoir Stimulation, 3 rd edition, John Wiley & Sons, Ltd, New York (2000) pp. 11-30 and 11-31; U.S. Patents US5330005; US5439055; US5501275; US5782300 The use of fibers in this way is described.

In using fibers to control proppant flowback in conventional hydraulic fracturing, those chosen parameters are chosen based on what is expected to happen in the fracture after the treatment is completed. Fibers are added at an optimum concentration to control proppant flowback without significantly affecting fracture conductivity. If glass fibers are used, then a suitable concentration is 1% by weight of the proppant. Under commonly employed conditions, this concentration is insufficient to cause bridging during pumping. Indeed, in conventional hydraulic fracturing, the fiber concentration is deliberately chosen so as not to increase the tendency to bridging during pumping. In most common hydraulic fracturing situations, fibers are added at the end of the treatment so that the proppant closest to the wellbore intermingles with the fibers. Indeed, the most critical of these treatments to prevent proppant flowback is the treatment of the fractured region near the wellbore. In traditional hydraulic fracturing, all proppant loading stages are sometimes treated with fibers; this can be done in wells when proppant flowback is the most critical issue, or when fibers are used for frictional pressure reduction purposes To be done. However, in these treatments, the fiber concentration scales linearly with respect to the proppant concentration (ie, if the amount of proppant is doubled, then the fiber concentration is doubled, etc.). In typical designs, the early proppant stage, proppant and fiber concentrations are very low; and the generation of screens is not expected, nor is it caused by these fibers, if any.

Fibers are sometimes added throughout a conventional hydraulic fracturing treatment for another reason: to aid in proppant transport, for example, when the fluid viscosity is very low. End screens are avoided in these treatments by careful design of the pretreatment job and especially careful choice of pumping times. For example, in these treatments, the packing volume is increased relative to typical job designs in order to ensure that sufficient fracture width is created before the proppant/fiber slurry enters the fracture. Additionally, fiber concentration was carefully tracked in the simulated job design, alerting engineers to the possibility of premature sieve formation. Finally, since the addition of fibers in all stages is critical to proppant transport in these designs, all stages must include fibers.

Thus, the use of fibers to control proppant flowback when the formation of end screens is not desired is characterized by two main principles: First, the amount of fiber required to control flowback is usually sufficiently low in conventional fracture designs , so that no end sieves are created. Second, although fiber is sometimes added throughout the process, for flowback control it is usually added at the end (or tailed in) of the process, usually in the last 10% of the process said fiber. This is because the physical properties of the proppant pack closest to the wellbore are of interest and must be controlled in order to prevent proppant flowback. The use of fibers to aid in proppant transport in conventional fracturing is characterized by careful job design and monitoring to prevent end-screening. In each case, the generation of end screens can be prevented as much as possible by either the inherent mode of use of fibers when the generation of end screens is undesirable, or by careful job design.

From this point in the description, except for Example 5, when we refer to "percent fiber" we mean "percent by weight of liquid in the slurry". For simplicity, assume that the density of the fluid used in the fracture fluid is approximately 8.4 pounds per gallon. A common proppant loading is 8 pounds of proppant in a slurry containing 1 gallon of liquid. This will be described as 8 pounds of proppant added, or 8PPA. In this case, if the fiber is added in an amount equal to 1% by weight of the liquor, then the amount of fiber will be about 0.5% by weight of the total slurry. Thus, when the amount of fiber is expressed as a weight percent on a liquid basis, it is different from a percent on a slurry basis, depending on the amount of proppant.

The processing of the present invention can utilize common equipment, chemical substance, personnel, and the mode identical with traditional processing is carried out in well field, but, if said equipment does not have the function of adding fiber, will carry out so to said equipment Improved to enable equipment to add fibers. In US patents US5501275 and US5782300 some methods for adding fibers are described. Preferably, the method of adding fibers is carried out by adding fibers to the proppant before the proppant is mixed with the fluid, to the fluid before the fluid is mixed with the proppant, or after the slurry is pumped to The fiber slurry is added at some stage before going downhole, but the invention is not limited thereto. Although the fibers are usually added to the fluid at about the same time as the proppant is added, the components can be premixed prior to work, or they can be mixed downhole.

In a preferred approach, treatments are designed to increase the likelihood of terminal screens even in the absence of fibres, and following a "data-fracture" or "mini-fracture", the initial treatment After some additional modifications were made to the design to further increase the possibility of the terminal screen, the treatment design was modified to include a high concentration of fibers in the fluid. When the proppant concentration is from about 0 to about 8 PPA, high concentrations of fibers are added at least to the early propping stages of this process. It is especially important to ensure that high concentrations of fiber are added to stages where the proppant concentration is from about 0.5 to about 6 PPA. Fiber is often added throughout the job. An increase in solids concentration due to leakage generally contributes to an increase in fiber and proppant concentration, and when the concentration of fiber and proppant increases beyond a critical value, a screen is created. Because the addition of a high concentration of fibers will reduce the fluidity of the proppant slurry, or even make the slurry immobile, which is usually avoided in conventional hydraulic fracturing. In the present invention, it is added intentionally. If sand control or proppant flowback control is not required, it may not be necessary to continue adding fiber after the end screen has been created.

Even in the absence of fibres, the treatment need not be designed in the first place to increase the possibility of terminal screening. The process can have a conventional design except that enough bridging promoting material such as fibers is added to create a screen. Also, fiber addition does not have to be early in the job. Adding fibers (gradually or stepwise) in increasing amounts of fiber until a screen is produced, or adding fibers suddenly at a high enough concentration at a later stage of the job to produce a screen, or increasing the amount of fiber continuously It is also within the scope of the present invention to add fibers in an incremental manner. Increasing the concentration of proppant in the slurry and/or increasing the injection rate combined with adding fiber in increasing amounts of fiber or starting fiber addition after pumping a fiber-free slurry also within the scope of the present invention. The methods of the present invention are advantageous when leakage is low because the tendency to create screens is greater when leakage is large. However, the present invention can also be used in any condition where fracturing is completed, including fracturing/gravel pack. For example, factors affecting leakage such as formation permeability or selection of one or more leakage additives (if used) can affect the optimum concentration of fibers desired, but are not limited to this optimum concentration of fibers desired ( or concentration distribution curve).

Combined stimulation/gravel pack with purposeful end screens can be accomplished in various ways. Some non-limiting examples include those described below. In the first method, a fracture with an end screen is formed first, the wellbore is cleaned, the screen is placed, and the gravel pack treatment is performed. In the second method, a strainer and special tools are placed before processing. End screen crevices are formed and filled with a tool set so that the injected filler and slurry enters the crevices but not the annulus; the tool is then adjusted so that the grout enters the annulus. The pumping rate is usually reduced to ensure filling of the annulus. In the third method, instead of using gravel and screens, additional techniques are used to prevent proppant or sand from being extracted. Said techniques are, for example, adding fibers to the proppant just before the fracturing operation, or using resin-coated proppants. Fiber and resin-coated proppants can also be used with screens.

The methods and fluids of the present invention can also be used in stimulation methods commonly referred to as "water-fracturing" or "water fracturing" or "smooth water fracturing". In hydro-fracturing, usually in order to reduce costs, use as little viscosifier and proppant as possible to produce hydraulic fractures. This is accomplished by utilizing very high pumping rates and high total slurry volumes. As usual, in traditional hydro-fracturing, the aim is to create as long a fracture as possible, however, if the operator wants to stop increasing in length and start increasing in width, then fiber sheets (a slug of fiber) or fiber and a high concentration of proppant.

Fibers or other bridging promoting materials may be added at a sufficiently high concentration to result in an end screen. However, in other embodiments, when bridging promoting material is used, the bridging promoting material may not be added in a manner sufficient to produce the end screen of the present invention. The densities of fibers, proppants and fluids can all be varied, so the amount of fibers will be high enough to result in end-of-sieve sieving, this can be done alone or in combination with filter cake degraders, depending on the Specific selection of agents and fluids. As described below with respect to the aqueous liquid and preferred fibers of the present invention, synthetic organic polymeric fibers have relatively low densities of about 1 to 1.5 g/cc. However, fibers of greater density may also be used, for example made of inorganic materials such as glass or ceramics; these fibers have a density more than twice that of synthetic organic polymeric fibers. When used with a filter cake degrader, the amount of fiber in the liquid/fiber/proppant slurry required to produce a terminal screen is most closely related to the fiber volume per volume of fiber/proppant mixture. Accordingly, the amounts of fibers described below should be adjusted for the specific component density involved. The denser the fiber, the higher the weight concentration required. In addition, aspect ratio, length, fiber diameter relative to proppant diameter all affect the amount of fiber (expressed as weight percent liquid in slurry) in the liquid/fiber/proppant slurry required to cause terminal sieving. As fiber diameter decreases or fiber length or aspect ratio increases, lower fiber weight percent (expressed as weight percent liquid in slurry) is required. Such adjustments are within the routine capabilities of those of ordinary skill in the art. Some particularly suitable fibers and other materials are described in US5330005, US5439055; US5501275; US5782300, but the present invention is not limited to these fibers and materials, and these patent documents are incorporated herein by reference.

What we refer to as "fiber" may be any fibrous material such as natural organic fibers, comminuted plant material, synthetic organic fibers (non-limiting examples are polyester, polyaramide (polyaramide), polyamide, novoloid or novoloid polymers), fibrillar synthetic organic fibers, glass fibers, carbon fibers, ceramic fibers, inorganic fibers, metal wires and mixtures thereof. Preferably, the fibrous material has a length of about 2 to about 30 mm and a diameter of about 5 to about 100 microns, most preferably a length of about 2 to about 30 mm and a diameter of about 10 to about 100 microns. The fiber cross-section need not be circular and the fibers need not be straight. If fibril fibers are used, the diameter of the individual fibrils can be much smaller than the previously described fiber diameters.

It has been found that at a concentration of synthetic organic polymeric fibers between about 1 and about 2 weight percent liquid, the fiber-containing slurry behaves like a standard fracturing fluid and can utilize standard oilfield pumping and mixing equipment to deal with. It has been tested with the downhole tool and it does not block the ports. Adding fibers to the early proppant stages will not significantly complicate the execution of the process.

However, as the fracturing fluid/fiber/proppant mixture enters the formation, the proppant and fibers will concentrate due to fluid leakage. At higher concentrations, the fibers greatly increase the propensity of the slurry to bridge. When the fiber concentration is increased to about 4 to about 5 weight percent due to leakage, the slurry has the appearance of wet pulp. It has been shown in laboratory and in field tests that about 4 to about 5 percent synthetic organic polymeric fibers in the liquid will clog channels 6 to 12 mm wide. Therefore, when fibers and proppants are concentrated in fractures due to fluid leakage, the slurry has a high tendency to bridge due to the presence of the proppant/fiber mixture and will form a sieve.

If fibers are used to help induce terminal sieving, then, when filter cake degradation has progressed to a fluid efficiency of about less than, for example, 20%, the fibers are typically at least in the first proppant stage, and the concentration is selected such that, The fiber/proppant slurry packs off (is no longer flowable), resulting in an end screen. It should be noted that in some methods of the present invention, the amount of fiber required to cause an end screen may be less than the amount of fibers typically used in a fracturing process to prevent proppant backflow without causing an end screen. This is because in the methods of the present invention, additional steps are used to degrade the filter cake and increase the concentration of the fiber/proppant slurry in the fracture. In other words, bridging is facilitated by deliberately increasing leakage. On the other hand, the amount of fiber used may also be greater than the amount of fiber typically used to prevent proppant flowback.

The amount of synthetic organic polymeric fibers is preferably adjusted over a range of from about 0.5 to about 2 weight percent to account for variations in fluid efficiency. 0.5 weight percent of synthetic organic polymeric fibers is generally considered a modest concentration that will not form a sieve. However, it is an object of the present invention to utilize fiber concentrations that result in sieves. In some cases, for example, if the fluid leakage coefficient is relatively high and the fluid efficiency is low, then the initial fiber concentration can be reduced to about that amount. Thus, this concentration is within the "normal" range for a "normal" treatment, but it is high for said treatment. On the other hand, if the fluid efficiency is very high, then the initial fiber concentration should be increased beyond the usual two percent to result in an end screen. Accordingly, the concentration of synthetic organic polymeric fibers in the present invention ranges from about 0.5 weight percent to about 3 weight percent, preferably from about 1 weight percent to 2 weight percent. In this context, by "high concentration" we mean a specific fiber concentration in a specific fluid/fiber/proppant combination that is high enough to significantly Increases the tendency to sieve.

Although in traditional hydraulic fracturing, the amount of fiber used is usually determined by the amount of proppant used, so that if the amount of proppant is changed at different stages, the amount of fiber is also changed, However, in the fluids and methods of the present invention, the amount of fiber used is more typically determined by the amount of liquid used, and more typically the amount of fiber is utilized as a constant weight percent of the liquid.

As the stiffness or hardness of the fibers increases, so does the tendency to begin bridging and forming a sieve. However, as hardness increases, fluid handling becomes more difficult. Fibers of various durometers or stiffnesses are readily available in the market. In addition, frictional pressure is often reduced by adding fibers during pumping. This is an added advantage, especially in conjunction with fracturing/gravel pack operations, where fluid is often pumped through, and often passed through, small orifices or passages. Selection can be readily made by one of ordinary skill in the art by considering the various advantages and disadvantages of different fibers in terms of cost, or availability, desired concentration, ease of handling, effect on frictional pressure, and other factors.

Although we refer to "end screens", the scope of this invention also includes the case where conventional process parameters are used to create conventional fractures of the desired length, and then, by starting to add filter cakes in a high concentration manner to degrade agent and/or filter cake degrader adjuvant and/or by continuously increasing the fiber concentration, resulting in sieving. Fibers can also be added to the packing in amounts comparable to those added during the proppant loading stage. Although gravel packing after fracturing is typically performed with screens in place, it is within the scope of the present invention to apply the fluids and methods to some treatments that do not employ screens. Although we have described the invention in terms of the production of hydrocarbons, production employed in injection wells, production wells, or storage wells, and production of other fluids such as water or brine, and the use of said fluids and methods also Belong to the scope of the present invention. Although we have described the invention in terms of using non-foaming fluids, the invention can also be used with foaming fluids or energized fluids (e.g., with nitrogen, carbon dioxide, or mixtures thereof); With some changes, the fiber concentration can be adjusted. It should also be appreciated that the fluids and methods of the present invention can be used to form end screens in multiple fractures, natural fractures or wormholes, etc. formed by acid treatment. Any of the methods of the present invention can be practiced using coiled tubing.

Another advantage of the fluids and methods of the present invention is that they give the operator additional parameters to adjust, that is, they allow flexibility in designing the sieving process. Thus, in situations where the operator does not wish to reduce the packing volume, slow the pumping rate, reduce the proppant loading, or make other design changes, the operator can utilize one of the methods of the present invention. Therefore, in carrying out the process of the present invention, it is preferable to design said treatment as such, that is, even if there is no method in the present invention, it is also likely to produce a sieve, and then adopt the method of the present invention in the work design One of the methods, in order to ensure the formation of a screen, however, the scope of the present invention also includes the following situations: without adopting one of the methods of the present invention to design a process that will not produce a screen, then in the work design Increase the use of one of the methods in the present invention. It is also within the scope of the invention to design and initiate pumping of a process that is not designed or expected to sieve at any point during the process and then decide during the process to cause sieving of the process to occur, Therefore, the design of the work is changed at the corresponding place to adopt one of the methods in the present invention.

It should be noted that although it is not desirable to create screens in the wellbore, in the annulus between the screen (if any) and the surface of the wellbore, or in perforations, it is desirable to The last of these areas are completely filled. That said, the ideal outcome would be to filter out in the fracture (where the origin of the screen is in the fracture) and then use the proppant/gravel to pack the above mentioned area.

Any proppant (gravel) can be used as long as the proppant (gravel) is suitable for the fiber, formation, fluid, and treatment desired. These proppants (gravels) can be natural or synthetic, covered (eg, covered with resin), or contain chemicals. It is possible to use more than one proppant in succession, or to use proppants of different sizes and different materials. Proppant means any granular material selected for a specific purpose, such as supporting fractures to keep them open, or gravel packing-completion to prevent or reduce the formation of microporosity . The proppant and gravel used in the same well or in different wells or treatments may be the same material and/or be of the same size. These materials are often referred to as proppants when placed into a fracture and gravel when placed within a perforation or wellbore, but in this context the term "proppant" Includes gravel. Typically, the average particle size of the proppant used is from about 10 to about 100 U.S. mesh, more specifically 40/60, 20/40, 16/20, 12/20 and 8/20 material , but not limited to these. Typically, the proppant is present in the slurry at a concentration of from about 1 PPA to about 25 PPA, preferably from about 1 PPA to about 16 PPA.

Some additives commonly used in packings and in the proppant loading stage of such treatments may be included as long as they are appropriate to the other ingredients and the desired outcome of the treatment. These additives may include: antioxidants, crosslinkers, anticorrosion agents, retarders, biocides and buffers. The wellbore being treated may be vertical, inclined or horizontal. These wellbores can be completed by casing, perforating, or tapping, with or without screens.

Cleavage agents suitable for use in the methods of the invention include, but are not limited to, enzymes such as galactomannanase (for cleaving polysaccharides according to galactomannan), such as alpha-amylase for cleaving fixed flour , cellulases and hemicellulases for the breakdown of cellulose, oxidizing agents such as persulfates, bromates, iodates, permanganates, percarbonates, perchlorates, perborates , hypochlorite, chlorine dioxide, chlorate (used to crack polymers by oxidation), but not limited to these. Additionally, these lysing agents can also be encapsulated to delay their release, as is known in the art. The use of encapsulation is advantageous because most or all of the polymer that is cleaved is located in the filter cake and is encapsulated, ie the cleavage agent acts later in the process. If the cleavage agent is not encapsulated, at least some of the cleavage agent will leak out and not contact the polymer in the filter cake, although some of the cleavage agent may flow back and contact the polymer when the fracture pressure is released. Another reason for the advantage of encapsulation is that the cleavage agent can be chosen so that it cleaves both the polymer and, in the case of viscoelastic surfactants, micelles . Encapsulation is also advantageous in that it delays the reaction. It is known in the art that different cleavage agents are more effective under different conditions (especially temperature).

A cracker adjuvant (or cracker activator) is used as a catalyst in order to enhance the cracking process and its performance, especially at lower bottom hole temperatures. Some examples of these cleavage agent auxiliaries are described in US Pat. No. 4,560,486 as tertiary amines, or mixtures containing tertiary amines, which aid in the oxidation of cleavage agents.

It will be appreciated that these splitting agents and splitting agent adjuvants may also be included in the job design for the purpose of degrading viscosifiers in the carrier fluid. These splitting agents and splitting agent adjuvants may be the same as or different from those used for the purpose of degrading the filter cake. The fluid must be able to transport the proppant until the treatment is complete. And the lysing agent, the lysing agent adjuvant, and the time and concentration of addition of these lysing agents and lysing agent adjuvant and the acid or solvent must be selected accordingly. For example, at any point during operation, a slow-acting splitting agent that is not active enough to degrade the filter cake during operation, but sufficiently active to degrade the viscosifier after pumping stops, can be slowly added at any point. Degradation occurs within accessible time and is independent of the addition of filter cake degraders or adjuvants. As another example, a lyser adjuvant may be included in the injection fluid during the time the filter cake is being let down so that the lyser adjuvant enters the filter cake; The cracking agent of the cake, and because of the cracking agent auxiliary agent in the filter cake, the filter cake degrades faster than the viscosifier.

The present invention can be practiced at any formation temperature, taking into account any cool-down that may occur, in which case the filler and fracture fluids and their components, especially filler and viscoelastic surfactants And micelles in fracture fluids have desirable properties, especially stability.

Example 1:

An end screen hydraulic fracturing job is designed using computer simulations through trademarked FracCADE software (Schlumberger's proprietary fracture design, prediction and treatment monitoring software) to predict the results that will be obtained. Said work was on a sandstone formation of 200mD permeability, 14ft thick, at a depth of 13,715ft, with a bottom hole static pressure of 9500psi and a temperature of 118°C. The proppant used was 20/40 mesh ceramic. The fracturing fluid was viscosified using 30 pounds of boron cross-linked guar per thousand gallons of 2% KCl in 2% KCl. Table 1 shows this working design. Pumping rate is measured in barrels per minute, fluid volume is measured in gallons, proppant concentration is measured in pounds of proppant per gallon of fluid, and injection time is measured in minutes. phase number pumping rate liquid volume proppant concentration injection time 1 (filler) 15 3500 0 5.5 2 15 1143 0.5 1.9 3 15 107 0.5 0.2 4 15 1201 1.5 2 5 15 1148 2.5 2 6 15 1102 3.5 2 7 15 1102 4.5 2.1 8 15 1002 5.5 2 9 15 1003 7.0 2.1 10 15 950 8.5 2.1 11 15 900 10 2.1 12 (flush) 15 4669 0 7.4

Table 1

Software trademarked FracCADE utilizes predetermined criteria to determine when a screen is to be generated. Two simulations were performed for this hydraulic fracturing job. The first simulation was a simulation of conventional hydraulic fracture tip screen formation with no added fibers. For this work, the FracCADE software predicts that when proppant attempts to enter a fracture with a size smaller than 2.5 times the proppant diameter, or at a proppant concentration of 22PPA, whichever occurs first, at this time sieve. In the second simulation, synthetic organic polymeric fibers were added to each proppant stage at a concentration of 0.6% by volume of the liquid in the slurry. In the case of this fiber, the FracCADE software predicts that when proppant attempts to enter a fracture whose size is less than 3.5 times the proppant diameter or at a proppant concentration of 18PPA, whichever occurs first, it will produce sieve. This is a relatively low fiber concentration, so this is a particularly rigorous experiment. The results of the experiment are shown in Table 2. Working parameters no fiber fiber Half Length of Supported Fissure (feet) 101.1 77.1 Width at wellbore supported (inches) 0.348 0.497 average supported width 0.235 0.375 Net pressure at the end of the job 649 1033 efficiency 0.509 0.533 Effective Conductivity (mD-ft) 1256 1947

Table 2

It can be seen that by adding fibers, the slit is shorter, wider and more conductive. By employing fibers, fluid efficiency is increased, which reflects the amount of proppant placed with a given amount of carrier fluid. If there is no fiber, then at 99 feet proppant is packed after 15 barrels of stage 6 have been pumped. Proppant is packed at 76 feet, if fiber, after 22 barrels of stage 4 have been pumped.

Example 2:

Prior to dynamic fluid loss testing, 1.5 inch diameter cores were osmotically saturated in experimental saline (2 gallons per thousand gallons of 50% tetramethylammonium chloride solution). A dynamic fluid loss device consists of a core holder designed to allow fluid to pass through one end face (front end) of the core and flow in such a way that some fluid will leak into the core Inside, fluid can be injected into the other end of the core (rear end) to measure the permeability of the core; the system is controlled by automated software. Saline was injected into the rear end of the core to measure the initial permeability. Borate cross-linked guar fluid (at a concentration of 20 pounds guar per 1000 gallons of fracturing fluid) was flowed over the surface of the core at varying pressures of about 500 psi for 30 minutes. (This causes some fluid to flow into the core, and if there is cake-forming material in the fluid, a filter cake will form on the core surface.) An automated fracture simulator is used to control the shear during actual processing. cutting rate. These fracture treatment parameters that need to be simulated for the dynamic fluid loss experiments are listed in Table 3. After a dynamic leak, regained permeability was measured by reinjecting the same saline into the back end of the core. parameter processing value Injection rate 15 pounds per minute (bpm) injection time 30 minutes Power index (n') 0.7 Fissure height 65 feet Crack length 75 feet Fracture width (at the wellbore) 0.75 inches distance from wellbore 1 foot

table 3

These experiments were performed at 52°C. Table 4 shows a comparison of laboratory results of dynamic leak tests simulating fractures with and without fluid loss control additive at a concentration of 30 pounds of fluid loss additive per 1000 gallons of fracturing fluid. This fluid loss control additive is a mixture of starch and granular flakes. The data demonstrate the effect of fluid loss control additives on permeability, leakage, and the depth at which leaked fluid penetrates into the formation. These data show that fluid loss is smaller and final permeability is greater when fluid loss control additives are used, both for leaks after injection (before cake formation) and for leakage after cake formation, The penetration depth of the fluid into the matrix is small. These results demonstrate how good fluid loss control additives can prevent or delay sieving. The test results of tests 2 and 4 are shown in graph form in FIG. 1 . These data will be used in the design of the method of the present invention. Figure 2 schematically shows (not to scale) how the presence or absence of a filter cake affects the extent of fluid leakage from fractures into the formation. In Figure 2, the filter cake [1] is formed from fluid loss control additives in the upper panel, rather than in the lower panel, which represents a filter cake where either no fluid loss control additive was used or the fluid loss control additive was removed. Condition. Therefore, if there is no filter cake, then more fluid will leak from the supported fractures [3] [2]. run Initial permeability (mD) Final permeability (mD) Spray (gal/100 sqft) Leakage after spraying (gal/100 sqft) Penetration Depth (inches) (without fluid loss control additives) 1 98 38 146 72 25 2 80 10 123 58 twenty one (with fluid loss control additive) 3 80 47 46 19 8 4 75 35 60 17 10

Table 4

Example 3:

Figure 3 shows some laboratory experiments used to illustrate the method of the present invention utilizing two stages of fluid loss control additive cracker (filter cake degrader). These are fluid loss experiments using the same method as in Example 1 at 52°C. It can be seen that in Experiment 1, when the first half contained the fluid loss control additive, the first splitting agent, and the splitting agent adjuvant (filter cake degrader adjuvant) for the second splitting agent present in the second half While still having the fluid loss control additive in the second half, there was no increase in fluid loss in the second half. In Experiment 2, when the first half was the same as in Experiment 1, but the second half contained no fluid loss control additive, the amount of fluid loss was significantly increased in the second half, indicating that the filter cake had been Serious destruction. In fracturing, this translates into bridging and/or reduced fluid efficiency and end screens. To ensure that this result was not solely due to the exclusion of fluid loss control additives from the second half of Experiment 2, another laboratory experiment was performed (see Figure 4) in which no The cracking agent or cracking agent adjuvant, however, the first stage includes the fluid loss control additive and the second stage does not include the fluid loss control additive. Figure 4 shows that in this case the flow increased slightly in the second stage, but this increase was very small compared to the results shown in Figure 3 . This clearly shows that the main factor is the lyser, especially the lyser adjuvant included in the first stage, the lyser adjuvant used for the lyser in the second stage, and the fluid It is not critical that the loss control additives remain in the second stage. The first phase of these experiments represents each packing or packing plus early proppant stage of the commercial simulation process; the second phase of these experiments represents the late proppant phase of the commercial simulation process.

Example 4:

Figure 5 is used to illustrate the effect of promoting bridging by adding fibers in addition to adding fluid loss control additives. The figure shows a specific embodiment where the packing forms a filter cake with cracking agent inside and then some fibers are added to the proppant stage to facilitate bridging and then added to the following proppant stage Additional lysing agents. (Schematics A through E show the change in fracture content from top to bottom as the simulation progresses; these schematics can be top or side views and are not to scale, The fractures are not necessarily of the same size in these successive schematics.) This sequence prevents the growth of the fractures and then removes the filter cake, which ultimately increases the flow rate of the fluids to be produced into the fractures. The viscosifier in the packing, the first cake degrader, the cake degrader adjuvant for the second cake degrader, and the fluid loss control additive were all the same as in the first half of Experiment 2 in Figure 2; The viscosifier in the carrier fluid was the same as the viscosifier in the packing, and the second cake degrader was the same as in the second half of Experiment 2 in Figure 2 . In Figure 5, "2-4PPA" means 2 to 4 pounds of proppant per pound of fluid ("pounds of proppant added" or stage of PPA), and "4PPA and above" means from 4PPA to the last The proppant stage plus the overflow stage.

The viscosified packing comprises a first cake degrader, a cake degrader adjuvant for a second cake degrader, and a fluid loss control additive. When the packing is pumped (Schematic A) and is at the leading edge of an enlarged fracture [4], a filter cake [5] is formed to control fluid loss and some fluid [6] leaks into the formation . In order to form a filter cake, sufficient packing must be pumped. In the 2-4 PPA stages (Schematic B), the carrier fluid comprises a synthetic organic polymeric fiber [7] added to each proppant [8] stage at a concentration of approximately 0.6% by volume of the fluid in the slurry , these synthetic organic polymer fibers inhibited the growth of the slit length. In a later stage (schematic C), the second cake degrader is introduced and, with the help of the (already present) cake degrader adjuvant for the second cake degrader, begins to degrade the filter cake. During pumping in the late proppant loading phase (Schematic D), the second filter cake degrader degrades the filter cake, causing progressively larger leaks. The end result (Schematic E) is a relatively short and wide fracture that has been screened out when and where needed with little or no filter cake and is well packed with proppant. Many variations can be made to the situation shown in these schematic diagrams, and the scope of the invention also includes, but is not limited to, the addition of fluid loss control additives, the addition of a first filter cake degrader, the filter cake for the second filter cake degrader Precise timing and amount of degradant adjuvant, second cake degrader, fiber. Other variations may include adding the above materials in a different order or in different combinations.

Example 5: Using registered trademark FracCADE software (Schlumberger proprietary fracture design, prediction and treatment monitoring software) to simulate three fracturing scenarios. In these protocols, the same fluid loss control additive as in Example 3, the cake degrader adjuvant for the second cake degrader when the same first cake degrader was present, the second cake degrader agent, and fiber. Fluid loss control additive was added in all three scenarios, and the rate of addition was designed to form a filter cake with 2 pounds of fluid loss control additive per one hundred square feet of fracture surface. Table 5 shows this working design. Pumping rates were both 15 barrels per minute; the packing and proppant loading stages were viscosified with 20 pounds of boron-crosslinked guar per thousand gallons of seawater; the overflow stage contained the same guar at Seawater has the same concentration but is not crosslinked. stage fluid gallons Proppant pounds Number of slurry tanks pumping minutes filler 5500 0 131 8.7 0.5PPA 1000 500 24.3 1.6 1.0PPA 1000 1000 24.9 1.7 2.0PPA 1000 2000 26.0 1.7 4.0PPA 1000 4000 28.1 1.9 6.0PPA 1000 6000 30.3 2.0 8.0PPA 1000 8000 32.4 2.2 10.0PPA 1500 15000 51.9 3.5 12.0PPA 3000 36000 110.2 7.3 overflow 3286 0 78.2 5.2

table 5

In Schemes 1 and 2, no filter cake degrader was used, nor was a filter cake degrader adjuvant. In Scheme 2, fibers were added to the 2-4PPA stage and at a rate of 0.8% by weight of the proppant. In Scenario 3, the packing included the first CDA and the CDA adjuvant for the second CDA, and the proppant loading stage from 2PPA contained the second CDA. Table 6 shows the results of these three scenarios. plan: 1 2 3 Are there fluid loss control additives in the packing? have have have Are filter cake degradants and adjuvants used? no no yes Filler Injection (gal/sqft) 0 0 46 Is fiber added in the 2-4PPA stage? no yes no Proppant Stage Injection (gal/sqft) 0 0 99 The half-length of the final supported crack 55.3 45.4 36.9 The width of the fracture that is finally supported in the wellbore 1.298 1.729 3.052

Table 6

It should be noted that the protocol includes sufficient pumping time to ensure filter cake formation. Fillers, fracture fluid, fracture fluid viscosifier, cracking agent (filter cake degrader), cracker adjuvant (filter cake degrader adjuvant), fluid loss control additive, proppant were employed in usual commercially handled amounts. From Scenario 1, it can be seen that when fluid loss control additive (FLA) is used but no filter cake breaking measures are taken, long narrow crevices are formed. When end sieving is performed in Scheme 2 by adding fibers, shorter, wider fissures are formed. When filter cake degradation is used to facilitate end sieving, the shortest and widest fissures are formed. A good job design should be a combination of Option 2 and Option 3.

The foregoing descriptions of specific embodiments of the invention are not intended to be exhaustive of every possible embodiment of the invention. Those of ordinary skill in the art will appreciate that various modifications can be made to the specific embodiments described herein, and these modifications are within the scope of the present invention.

Claims (12)

1. method that forms screen in subsurface formations stimulation treatment process, this method comprises: inject proppant particulates slurry with the pressure that is higher than frac pressure in carrying fluid, comprise that also adding bridge joint in said slurries promotes material.

2. method that in subsurface formations stimulation treatment process, forms screen, this method comprises: inject proppant particulates slurry with the pressure that is higher than frac pressure in carrying fluid, so that form one or more cracks, this method may further comprise the steps:

A) inject the filler fluid, this filler stream body is used to form filter cake;

B) inject one or more first slurry stage, this first slurry stage comprises the proppant in the carrying fluid;

C) when injecting one or more second slurry stage, utilize the filter cake degradation agent to make filter cake degradation, second slurry stage wherein comprises the proppant in the carrying fluid.

3. according to the method for claim 2, wherein, filter cake is that these materials are by one or more are formed in the following material: water-soluble polymer, crosslinked water-soluble polymer, fluid loss additive and their mixture.

4. according to the method for claim 2 or 3, wherein, the filter cake degradation agent is selected from following this listed group material: oxidant, enzyme, acid and their mixture.

5. according to each method of claim 2 to 4, wherein, the filler fluid comprises a kind of in material of this group of listing below, this group material is: fluid loss additive, filter cake degradation agent, filter cake degradation agent assistant and their mixture, as long as for included filter cake degradation agent, do not comprise that the filter cake degradation agent assistant at it gets final product; One or more first slurry stage comprise in this group material of listing below a kind of, this group material is: fluid loss additive, filter cake degradation agent, filter cake degradation agent assistant and their mixture, as long as for the filter cake degradation agent that has in included or the filler, do not comprise that the filter cake degradation agent assistant at it gets final product; One or more second slurry stage comprise a kind of in material of this group of listing below, and this group material is: filter cake degradation agent, filter cake degradation agent assistant and their mixture.

6. according to each method of claim 2 to 5, wherein, filler fluid and one or more first slurry stage all comprise: fluid loss additive, the first filter cake degradation agent, be used for the filter cake degradation agent assistant of the second filter cake degradation agent, the second filter cake degradation agent wherein has more activity than the first filter cake degradation agent under treatment conditions; And one or more second slurry stage, this second slurry stage comprises the second filter cake degradation agent.

7. according to each method of claim 2 to 6, wherein, filter cake comprises polymer, and this polymer is subjected to enzymatic and degraded oxidation under treatment conditions; The first filter cake degradation agent is present in the filler, and comprises the enzyme that is used to make the said polymer degraded; The second filter cake degradation agent is present in one or more second slurry stage, and comprises the oxidized compound that is used to make the said polymer degraded; The second filter cake degradation agent assistant that is used for the second filter cake degradation agent is present in filler fluid, one or more first slurry stage and one or more second slurry stage, and comprises tertiary amine.

8. according to each method of claim 2 to 7; wherein; filter cake comprises the solid particle compound of theobromine dissolving; the second filter cake degradation agent is present in one or more second slurry stage and comprises a kind of acid, and this acid can be dissolved the solid particle compound of at least a portion theobromine dissolving under treatment conditions.

9. according to each method of claim 2 to 8, wherein, one or more filler fluids, one or more first slurry stage, one or more second slurry stage comprise a kind of bridge joint and promote material.

10. according to each method of aforementioned claim, wherein, wellbore treatments is selected from: then carry out gravel pack after the fracturing, fracturing, and unite fracturing and the gravel pack of carrying out.

11., wherein, before wellbore treatments, sandy soil control filter screen is placed into the position according to each method of aforementioned claim.

12. according to each method of aforementioned claim, wherein, the fluid composition of said slurries is selected from this group material of listing below, this group material is: emulsion, foam, energized fluids.

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